The brain functions by forming a complex network from a great variety of neurons. Its failure may result in various neurological diseases. To treat such diseases, transplantation and regeneration therapies are currently investigated. The most important thing in these therapeutic methods is to correctly identify various types of neurons in transplantation materials. Furthermore, from the viewpoint of improvement of safety and therapeutic effect, it is desirable to isolate only the type of cells that are needed for transplantation.
The cerebellum works on smooth motor functions such as regulation of balance, posture, and voluntary movement. The failure of cerebellar function due to cerebellar tumor, cerebellar vermis degeneration caused by chronic alcoholism, spinocerebellar degeneration, or such results in dynamic ataxia and balance disorder. Functional recovery can be achieved by replenishing lost neurons and reconstituting the network. There are about five types of neurons in the cerebellum including Purkinje cell, and formation of a proper network of the respective neurons according to organogenic program enables neurotransmission.
There is an area called “dorsal horn” in the dorsal spinal cord. Dorsal root ganglion neurons that detect stimuli from the periphery transmit signals to the dorsal horn interneurons, and the signals are further transmitted to the brain. The dorsal horn contains excitatory glutamatergic neurons and inhibitory GABA neurons. The balance between the two adequately regulates the signal transmission. Inactivation of GABA neurons results in chronic pain, etc.
The development of spinal cord and cerebellar GABA neurons is being studied, and their origin is nearly elucidated. However, there are few markers to identify their progenitor cells, and no cell-surface marker has been identified. Thus, techniques for isolating viable progenitor cells have not yet been developed.
The 65B13 gene is known to be transiently expressed in dopamine-producing neuron progenitor cells after the termination of cell division (see Patent Document 1); however, there is no report published on the connection between the gene and GABA neuron. Furthermore, it has been reported that the types of spinal cord interneurons and Purkinje cells can be identified by using the expression of the Corl1 or Corl2 gene as an indicator, respectively (see Patent Documents 2 and 3). However, to date there is no known marker that can selectively identify GABA neuron progenitor cells. The transcription factor Ptf1a is known to be expressed in GABA progenitor cells; however, it is a transcription factor, and there is no known membrane protein that is useful as a selection marker (Non-Patent Documents 1 and 2).    Patent Document 1: WO2004/038018    Patent Document 2: WO2006/022243    Patent Document 3: WO2006/082826    Non-Patent Document 1: Glasgow S M, Henke R M, Macdonald R J, Wright C V, Johnson J E. Ptf1a determines GABAergic over glutamatergic neuronal cell fate in the spinal cord dorsal horn. Development. 2005 December; 132(24):5461-9.    Non-Patent Document 2: Fuse T, Matsuo N, Sone M, Watanabe M, Bito H, Terashima T, Wright C V, Kawaguchi Y, Nakao K, Nabeshima Y. Ptf1a, a bHLH transcriptional gene, defines GABAergic neuronal fates in cerebellum. Neuron. 2005 Jul. 21; 47(2):201-13.